Discovered in the 1990s, orexin (or hypocretin)-containing neurons in the lateral hypothalamus are now receiving considerable attention for their possible role in regulating motivated behavior for drugs of abuse. Indeed, previous studies from our laboratory and others have shown that the orexin-1 receptor antagonist, SB- 334867 (given systemically or directly infused into the insular cortex) decreases intravenous nicotine self- administration in rats. However, the role of orexin-2 (OX2) signaling in mediating nicotine reinforcement is poorly understood. Further, little is known about the effects of abstinence on orexin signaling following repeated nicotine consumption and its precise role in driving relapse. These are critical issues since human smokers often feel 'cravings' and subsequently relapse following intermittent periods of abstinence. Here, the first aim of this proposal is to assess intravenous nicotine self-administration in mice lacking OX1 receptors (OX1-/-), test whether viral-mediated re-expression of OX1 receptors in the insular cortex of OX1-/- mice rescues deficits in nicotine intake, and investigate the role for OX2 receptors in nicotine reinforcement using novel pharmacological agents and OX1-/- mice. Given the susceptibility of addicts to relapse to smoking after periods of cessation, the goal of Aim 2 will be to determine the effectiveness of selective OX1 and OX2 receptor antagonists on nicotine seeking and taking behavior following different periods of drug abstinence (0, 7 or 30 days) in well trained rats. Wit drug-associated cues often elicitors of relapse for smokers, Aim 3 will investigate the effects of nicotine abstinence on the associative properties of orexin cell firing in the lateral hypothalamus This aim will entail electrophysiological recordings in behaving animals to determine if the activity of putative orexin neurons is altered following nicotine-paired cue presentation after extended periods of abstinence. Collectively, these experiments will provide important insight into the psychobiological mechanisms underlying nicotine addiction, and promise to yield a novel therapeutic strategy for treating human smokers.